Process for improving vat dyed nylon fibers



Patented Feb. 13, 1951 PROCESS FOR IMPROVING VAT DYED NYLON FIBERSWilliam Henry Sharkey, Wilmington, Del., as-

signor to E. I. du Pont de Nemours & Company, Wilmington, Del., acorporation of Delaware No Drawing. Application July 22, 1949, SerialNo. 106,326

3 Claims. (on. 8-34) This invention relates to textile fabrics and moreparticularly to dyeing nylon fibers and fabrics.

, The synthetic linear polyamides known as nylon and the production offibers and fabrics therefrom have been described in a number of UnitedStates patents and in particular in 2,071,250; 2,071,253 and 2,130,948.These fiberforming polycarbonamides described in the previouslymentioned patents are obtained by several methods, for example, byself-polymerization of a monoaminomonocarboxylic, e. g., 6- aminocaproicacid; by reacting in substantially equimolecular proportions a dibasicacid, e. g., adipic or sebacic acid with a diamine, e. g.,hexamethylenediamine or with a monoaminomonohydric alcohol, e. g.,monoethanolamine, it being understood that thesereactants can bereplaced by their equivalent amide-forming derivatives. In thesepolyamides the average number of carbon atoms separating the amidegroups is at least 2. The preferred polyamides have an intrinsicviscosity of at least 0.4 (defined as in Patent 2,130,948) and a unitlength (definedin Patent 2,071,253 and Patent'2,130,948) of at least 7.

The filaments, yarns, fibers, fabrics and the like, madefrom the nylonpolymers described above, which may be referred to more briefiy as nylontextile articles, are difiicult to dye to give even colors which areresistant to the deleterious effects of light. More particularly, thesedifiiculties are those pointed out in an article by Saville in AmericanDyestufi' Reporter (January 23, 1946, page 55) who notes that the vatcolors, while of paramount importance in producing dyeings with maximumfastness to light and washing on cotton and other cellulosic materials,exhibit indifferent afiinity when applied to nylon by methods commonlyused. Although, as further noted in the mentioned article, vat colorscan be applied successfully to nylon at high temperature dyeing inshades very fast to washing, and to other wet processing and tocracking, the fastness to light of these colors m particularlydisappointing in that many were badly faded in 10 to 30 hoursFade-Ometer exposure and no individual dyestufi is unaffected after 100hours exposure.

It has. been assumed that the reason for rapid fading of vat colors onnylon is due to poor penetration of the fiber with dye and oxidizingagents.

However, refinements in such procedure, e. g., by the use of penetratingoxidizing agents, gave no improvements in light fastness. Steaming atelevated temperatures has given dyeings of im 'crocking. Such treatmentgives a major proportion of the color on the fiber surface in the formof gross aggregates which are easily washed or rubbed off. The steamingtreatment accordingly brings about a migration of the color from thefiber interior to the surface, the size of any dye particles within thefiber being essentially unaffected and remaining below the limit ofresolution of the optical microscope. Other agents, such asp-nitrophenol, have been suggested to produce better light fastness.However, as observed in the article mentioned above, no particular valueis seen in such aftertreatment since the very poor rubbing fastness ofthe dyeing and the cumbersome aftertreatment are most unsatisfactory.

This invention has as an object a vat dyed nylon textile fiber which islight fast and which is fast to washing, and to rubbing. A furtherobject is a method for obtaining these vat dyed nylon fibers. Otherobjects will appear hereinafter.

I have discovered that vat dyed nylon textile fibers which contain thevat dye in the interior of the fiber in a particle size of from 0.2 to 5microns are fast to light, to washing and particularly to rubbing. Inthe preferred embodiment of the invention, illustrated in Examples I toIII, these light fast nylon textiles are obtained by dyeing the textilewith a vat dye and then heating the dyed yarn in an aqueous solution ofan aliphatic polyhydroxy compound containing 2-6 carbons and having 2-3alcoholic hydroxyls, and preferably an aqueous ethylene glycol solution.In a further embodiment, illustrated in Example V, the procedureinvolves intermittent heating of the dyed nylon, which is moistened withwater, in mineral oil heated to temperatures of the order of -210 C.

The nylon textile article is dyed with the vat dye by any conventionalprocedure. For example, a nylon text le article may be placed in anaqueous dyebath which contains the dye in a reduced form. Generally thedyebath is at an elevated temperature, e. g., 50-100 C. for times of afew minutes to several hours. The nylon is removed from the bath and thevat dye insolubilized or fixed by subsequently oxidizing by air or mildoxidizing agents. The dyed article generally conta ns the dye in anamount of 0.1 to 10% based on the weight of nylon, and the dye ispresent in finely divided particles the size of which is below the limitof resolution of the light microscope which is less than 0.1

articles can contain from 10% to 90% of the ethylene glycol. The optimumeffects, however, are more easily obtained when 50% to 90% of theethylene glycol is present. .The temperature can be varied from 100 to150 C. although 110 to 130 C. are preferably used. When temperatures ofabove the normal reflux temperature are employed, the treatment may beeither carried out in sealed pressure-resistant containers, or inertsalts such as sodium chloride may be added in amounts sufliclent toincrease the boiling point of the aqueous ethylene glycol. The lattermethod is simpler and therefore preferred. The

time necessary for the increase in particle size of the vat dyestuflvaries with the temperature. In general the time should be at least 2minutes and preferably an hour. Usually times of longer than 10 hoursare unnecessary.

Although the dye particle size may be increased by the simple treatmentin a hot aqueous ethylene glycol bath as shown in Example I,intermittent heat treatment as described in the remaining examples ispreferred in view of the fact that it better promotes the growth oflarger dye particles in the interior of the fibers. This process simplyinvolves the heating of the dyed nylon in a number, e. g., 10 or more,of cycles such that the total time the nylon is heated above 100 C. inthe aqueous ethylene glycol bath is at least 2 minutes. The time thedyed fiber is cooled is generally at least one-fourth of the time it isunder heat treatment in the aqueous bath. The temperature of the inertmedium in which the fibrous material is cooled is not particularlycritical but is below 100 C., for example. between 98 C. and C.; andpreferably below 50 C., for example, to a temperature between 20 C. and50 C.

The following examples, in which the parts given are by weight, furtherillustrate the practice of this invention.

Example I A piece of nylon taffeta. woven from semi-dullpolyhexamethylene adipamide nylon yarn (i. e., containing 0.3% T102) wasdyed with a red vat dye powder of Color Index No. 1162 by the followingprocedure: A solution of 400 parts of water, parts of 20% sodiumhydroxide and 0.1 part of dye was heated to 80 C. To this was added 4parts of sodium formaldehydesulfoxylate and 1 part of sodiumhydrosulfite. After mins. at 80 C., the dye bath was heated to 90 C. and10 parts of the nylon fabric was added. The nylon was gently agitatedfor 45 mins. at 90 C. and then removed from the bath and rinsed. It wasthen acidified in a bath consisting of 200 parts of water and 5 parts of2% acetic acid. After rinsing it was allowed to air oxidize and then wassoaped in a solution containing 2 parts of soap in 200 parts of waterfor 30 mins. at 90 C. It was then rinsed and dried A section of thecloth amounting to 1 part was cut and heated to the boiling temperaturein a bath consisting of 75 parts of ethylene glycol and 25 parts ofwater. The boiling temperature was 118 C. Boiling was continued 1 hourand during this time water was added occasionally to maintain constantvolume of solution. The nylon was then removed, rinsed, dried and soapedin a solution of 2 parts of soap in 100 parts of water.

The piece which had been boiled in ethylene glycol was exposed in aFade-Ometer alongside a piece cut from the same section of dyed clothwhich had not been treated. After 20 hours exposure, the ethylene glycoltreated piece showed a very slight color change that was justperceptible to the unaided eye whereas the untreated piece showed veryserious fading and had turned brown. No further change occurred in theethylene glycol treated section on continuation of the exposure for 100hours, as compared with continued fading of the untreated piece whichwas light tan at the end of 100 hours. The dye particle size of theethylene glycol treated yarn was about 0.2 micron as compared to lessthan 0.1 micron for the control.

Example II Nylon taffeta woven from yarn which was entirely free ofdelusterant was dyed exactly as described as in Example I. The cloth wascut into two equal portions. One of the pieces was treated in a boilingbath composed of '15 parts of ethylene glycol and 25 parts of water andsaturated with salt. The boiling point of this solution was 130 C. Thecloth was treated by im mersing it for 15 seconds in the boilingsolution followed by removal and immersion in water at room temperature.This heating cycle was repeated for a total of times, i. e., the totaltime of immersion in the boiling bath was 20 minutes. The cloth was thenlaundered for 30 minutes in a Launder-Ometer at a temperature of 150 F.The laundered cloth was rinsed well and dried. The piece which had beentreated in boiling ethylene glycol was expo ed in the Fade-Ometeralongside the untreated piece. The treated sample showed only a veryslight change in color depth in 20 hours as compared to a very seriouscolor change with the untreated cloth which turned brown. Furtherexposure showed very little further change in color of the treatedsample as compared to serious color degradation of the untreatedcontrol, which was a light tan after hours. Examination of fiber crosssections under the microscope showed that the treated sample containeddye particles in ide the fiber of about 0.2 to 0.5 micron in diameter.Similar micrographs of the untreated sample showed that the particleswere too small to be detected by the light microscope and therefore werepresent as particles less than 0.1 micron in diameter.

Esample 111 Nylon taffeta woven from yarn completely free fromdelusterant was dyed with 5% of a yellow vat dye powder of Color IndexNo. 1132 by the procedure described in Example I. A section was treatedas in Example 31 except with boiling 75% aqueous ethylene glycol C.) andthe treated section was exposed in the Fade-Ometer together with an unreated section as a' control. The treated section did not fade upon 20hours exposure, whereas the untreated section faded very markedly.Exposures up to 100 hours caused very little change in the treatedcloth, whereas the exposed portion of the untreated dyed cloth wasbleached white. The particle size of the dye in the glycol treatedsample was about 0.2 micron as compared to less than 0.1 micron in thecontrol.

Example IV Nylon taffeta woven from yarn completely free fromdelusterant was dyed with of a violet vat dye powder of Color Index No.1163 by the procedure described in Example I. A section of the cloth wastreated as described in Example 11 and the treated section exposed inthe Fade- Ometer together with the untreated section as a control.Although the treated section did lose color upon 20 hours exposure, thecolor loss was very much less than that of an untreated control whichshowed very bad fading. The particle size in the dye of theglycol-treated sample was about 0.2 to 0.3 micron as compared to lessthan 0.1 micron in the control.

Example V A piece of nylon fabric woven from yarn that was completelyfree of delusterant was dyed as described in Example I. The fabric wasthen cut into two pieces. One piece was allowed to stand in water at 100C. for 15 minutes and then removed, pressed dry with a paper towel, andimmediately immersed into Nujol (mineral oil) heated to 190 C. for aperiod of 2-5 seconds. The nylon was then removed, rinsed in petroleumether, dried, and again allowed to stand in water for 15 minutes. Thisheating cycle was repeated five times, i. e., was given a total of fiveimmersions in Nujol (mineral oil) at 190 C. This piece was thenthoroughly laundered with a 2% soap solution to remove surface coloragglomerates and then rinsed and dried. Microscopic examination of fibercross sections showed the dye present inside the fibers of particle sizeof 0.2 microns. Similar cross sections of the untreated piece showed thecomplete absence of dye particles large enough for detection (i. e.,less than 0.1 micron). Exposure of the treated piece together with theuntreated control in the Fade-Ometer showed that the nylon section thathad been treated in the mineral oil faded much less in hours than theuntreated control, and this difference was even greater after 100 hoursFade- Ometer exposure.

The light durability of all vat dyes in nylon is improved when thesedyes are present as particles about 0.2 micron or larger in size. Thesedye particles are smaller than 0.1 micron when applied to nylon by thestandard methods. Nylon which contains larger dye particles showsimproved fastness to light and when these particles are 0.2 micron orlarger the light durability approaches or surpasses the well knownextremely good light fastness of these colors on cotton. Particleslarger than 5 microns are not desirable since fibers containing suchlargeparticles-show reduced tensile strength. Accordingly the preferredcompositions contain particles 0.2 to 5 microns in size.

The process for preparing nylon yarn containing large dye particles asdescribed herein can be employed to grow dye particles in nylon to anydesired size by variation of (l) the number of heating cycles, (2) theheating time during each cycle, and (3) the temperature employed. Thesevariables are all interdependent. Particle size the temperature employedduring each heating cycle, and decreases as the time of each heatingcycle is decreased. Temperatures above 120 C. can be obtained withethylene glycol by saturating with salt and heating to boiling or by useof pressure equipment. Temperatures can be increased at atmosphericpressure by increasing the amount of glycol up to In the preferredconditions the dyed cloth is immersed for 5-15 seconds in the boilinsolution followed by cooling for about the same length of time in waterat a temperature of from 20 C. to 98 C., and repeating this heatingcycle for 10 to 200 times. The temperature of the boiling bath can bebetween 100 C. and 150 C. using glycol concentrations of 10% to 90%.Preferred temperatures of the boiling bath are -150 C. and the preferredbath composition is from 50% to 90% ethylene glycol. This bath may besalt free or saturated with salt, such as sodium chloride or sodiumsulfate which is nonreactive with the nylon under the conditionsemployed. Similar improvement is obtained when aliphatic polyhydricalcohols of 2 to 6 carbons and containing generally 2 to 3 hydroxylsother than ethylene glycol are used in the above general procedure.These include glycerine, thiodiglycol, diethylene glycol, andtriethanolamine. Other compounds which have also been found useful arecaprolactam, Cellosolve (monoethyl ether of diethylene glycol) andethylene carbamate. These compounds are preferably present in aqueoussolutions in concentrations of 10-90% and preferably 50-90%. When theprocess is carried out by means of mineral oil the total time of heatingat the higher temperatures, e. g., 110 C. to 210 C. can be reduced to aslow as 10 seconds.' The best results are obtained when the periods ofheating with the oil range from 5 to 25 seconds and the period ofcooling from 5 to 60 seconds or more with the total time of heatingwithin the range of from 10 seconds to 2 minutes.

The present invention presents a valuable advance in the preparation ofdyed nylon fabrics. The dye is particularly stable to the deleteriouseffects of light, washing and rubbing in view of the fact that it isdispersed as large particles in the interior of the fiber. The inventioncan be readily carried out in various forms of available apparatus andon the less conventional forms of nylon, e. g., hollow nylon filaments.The dyed nylon articles of this invention are particularly useful forfabrics, e. g., upholstery and similar applications where light fastnessis required.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that I do not limit myself to the specific embodimentsthereof except as defined in the appended claims.

I claim:

1. A process for obtaining an improved dyed nylon fiber, said processcomprising dyeing the nylon fiber with a vat dye, and then subjectingthe dyed fiber to alternate heating, at a temperature of from 100 C. toC. in a mixture of water and aliphatic polyhydric alcohol whichcontains. from 10% to 90% of said alcohol, said alof the dye increaseswith an increase in the number of heating cycles and with an increase ofcohol having from 2 to 6 carbon atoms and containing from. 2 to 3alcoholic hydroxyls, and cooling of the fiber in an inert medium to atempera- 2. A process for Obtaining an improved dyed nylon fiber, saidprocess comprising dyeing the nylon fiber with a. vat dye, and thensubjecting the dyed fiber to alternate heating, at a temperature of from100 C. to 150 C. in a mixture of water and ethylene glycol containingfrom 10% to 90% ethylene glycol, and cooling of the fiber in an inertmedium to a temperature of from 98 C. to C., and continuing saidalternate heating and cooling until the fastness tolight and to washingand to rubbing of the dyed fiber is substantially increased.

\ 3. A process for obtaining an improved dyed nylon fiber, said processcomprising dyeing the nylon fiber with a vat dye, immersing the dyedfiber alternately, with a period of from to seconds between thealternations, in a boiling aqueous solution of ethylene glycol of fromto ethylene glycol concentration and in water at a temperature of from98 C. to 0 C., and continuing the process until the fastness to lightand to washing and rubbing of the dyed fiber is substantially improved.

WILLIAM HENRY SHARKEY.

5 REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS 10 Number OTHER REFERENCES Amer. Dyestufi Reporterfor January 28, 1946, 20 page 55. Available in Scientific Library ofPatent Oflice.

1. A PROCESS FOR OBTAINING AN IMPROVED DYED NYLON FIBER, SAID PROCESSCOMPRISING DYEING THE NYLON FIBER WITH A VAT DYE, AND THEN SUBJECTINGTHE DYED FIBER TO ALTERNATE HEATING, AT A TEMPERATURE OF FROM 100* C. TO150* C. IN A MIXTURE OF WATER AND ALIPHATIC POLYHYDRIC ALCOHOL WHICHCONTAINS FROM 10% TO 90% OF SAID ALCOHOL, SAID ALCOHOL HAVING 2 TO 3ALCOHOLIC HYDROXYLS, AND CON-TAINING FROM 2 TO 3 ALCOHOLIC HYDROXYLS,AND COOLING OF THE FIBER IN AN INERT MEDIUM TO A TEMPERATURE OF FROM 98*C. TO 0* C., AND CONTINUING SAID ALTERNATE HEATING AND COOLING UNTIL THEFASTNESS TO LIGHT AND TO WASHING AND TO RUBBING OF THE DYED FIBER ISSUBSTANTIALLY INCREASED.